Fluid supported load systems

ABSTRACT

A method of pressure control for fluid cushion supported loadbearing platforms, the system comprising sensors responsive to, and transmitting signals indicative of pressure fluctuations within the fluid support cushion, as a control flow to a fluidic network, the resultant output from the fluidic network being applied to a device which regulates the flow of pressurized fluid to the support cushion, thereafter providing control of the pressure therein.

tates atent Tenn et mil,

T IUUTD SUPPORTED LUATI' SYSTEMfi Inventors: Michael A. M. Young, Wincanton; George 1111. lDunsmuir, Yeovil, both of England British Hoverernlit Corporation Limited, Yeovil, Somerset, England Filed: Jan. 119, 1970 Appl. No: 3,000

Assignee:

Foreign Application Priority Date:

Jan. 16, 1969 Great Britain ..3,299/69 US. Cl .180/118, 104/23 FS, 180/121,

180/124 int. Ci ..l ..B60v M00 FieldoiSean-ch ..180/118, 121, 124

References Cited UNITED STATES PATENTS Cockerell 180/1 18 5] Mar. 14, B972 3,340,943 9/1967 Hirsch I 80/1 18 3,373,837 3/1968 Guienne "180/118 3,439,772 4/1969 Giraud 1 80/1 18 3,513,935 5/1970 Noble ..l80/124 Primary Examiner-A. Harry Levy Attorney-Larson and Taylor [5 7] ABSTRACT A method of pressure control for fluid cushion supported load'bearing platfonns, the system comprising sensors responsive to, and transmitting signals indicative of pressure fluctuations within the fluid support cushion, as a control flow to a fluidic network, the resultant output from the fluidic network being applied to a device which regulates the flow of pressurized fluid to the support cushion, thereafter providing control of the pressure therein.

10 Claims, 8 Drawing Figures PATENTEDHAR 14 I972 SHEET 6 OF 6 IFILUIID SUPPORTED LOAD SYSTEMS at parasitic frequencies.

According to the invention there is provided a pressure control system to obviate parasitic oscillations in fluid supported load bearing platforms wherein variations in pressure within a fluid pressure cushion are sensed by at least one fluidic element, the output from which is utilized to actuate means for controlling the flow of fluid to said fluid cushion, thereby effecting a control on the pressure variations within said fluid cushion.

In a further embodiment, the invention resides in a pure fluid supporting system comprising a load carrying platform, one or more fluid support cushions disposed beneath said platform, a conduit conveying a supply of pressurized fluid to said support cushion or cushions, valve means positioned relative -to said conduit to control flow through said conduit, sensor means positionably responsive to pressure variations occurring within said fluid support cushions, fluidic control means utilizing signals from said sensor means to control the operation of said valve means.

A first method of utilizing the invention is shown, by way of example only, in

FIG. 1 of the accompanying drawings, which discloses diagrammatically a simple control system for a single hover pallet.

A second utilization ofthe invention is disclosed in FIG. 2, where a more sophisticated system is employed to control a multi-cushion hover pallet;

FIG. 3 shows diagrammatically a modified form of system sensitive to movement ofa sprung mass.

FIGS. 4, 5 and 6 show further examples of the type of air cushion vehicle to which the control system of the invention may be used to advantage.

FIGS. 7 and 7A disclose two of many suitable types of amplifier for use with the invention.

Referring to FIG. l, a brief description of the hover pallet assembly is as follows:

A platform I has a diaphragm 2 of flexible material attached to its underside by airtight joints at points 3 and 4. It is to be understood that only one half of an air cushion pad is illustrated in the drawing, and that the diaphragm 2 is symmetrical about a centerline 5, thus the securing point 3 is at the center of the diaphragm and the securing point 4 is at the periphery ofthe diaphragm.

The diaphragm is made of any flexible impermeable material, for example, natural rubber, neoprene or polyurethane, and is moulded to a convoluted shape with convolutions concentric with the central fixing point 3. The convolutions when the diaphragm is retracted divide the air space above the diaphragm into a number of concentric annular spaces. A lip I2 defines an annular air escape passage with the ground line 10.

Air at superatmospheric pressure is supplied to the space between the diaphragm 2 and the platform by way of supply pipe 11 and orifice 6. An orifice 7 in the diaphragm 2 provides a passage for the air into the cushion area 8.

When the air supply is shut off, the platform I rests upon supports 9 above the ground line 10. In this condition the air on each side of the diaphragm 2 is at atmospheric pressure, and the diaphragm assumes its moulded convoluted shape with its convolutions substantially equally spaced above and below a straight line joining the central securing point 3 and the periphery point 4, and it is clear ofthe ground.

The fluidic control system shown utilizes a single proportional amplifier l3. This amplifier may, of course, be of any conventional type as there are numerous suitable types availa ble, e.g., fully vented jet interaction beam deflection am plifiers (FIG. 7), vented pressure interaction beam deflection amplifiers, wall attachment devices, and vortex amplifiers (FIG. 7A),etc.

It must also be understood that, while only one element is depicted, several may be employed to give extra amplification of output signals, together with any necessary feedback stabilization.

The initial problem to overcome originates in the pressure area defined by the platform, diaphragm and ground. As cushion pressure increases, the fluid at a certain stage becomes active, that is, a parasitic oscillation develops within the fluid support pad. The pressure at which this occurs may be dependent upon many variables, for example, weight carried by the platform, ground clearance, position of C. of 6., etc.

In operation, when this oscillation or bounce" occurs, a pressure fluctuation is sensed within chamber 14 by a pressure sensor, this again may be of any convenient type, in the embodiment a pitot sensor 15 is used.

The fluidics are supplied with power fluid from a tapping 16 in the main supply conduit 11, the flow is first filtered at 17 before passing through supply lines 18, 19 and 20 to the fluidamplifier 13. Pressure line 18 also supplies a pressure flow to pitot sensor 15 at supply pressure. This ensures that no dust or dirt particles can pass from the cushion area, back up through line 18 into the fluidic system. Any parasitic pulsing within the pressure support pad transmits pressure waves through sensor 15, line 18 and control lines 21 and 22 to control jets 23 and 24 of element 13.

By virtue of the delay introduced into control line 21 by capacity 25, the pressure wave affects control jet 23 before controljet 24L In this embodiment, an adjustable bias pressure is continuously fed through line 20 and variable restrictor 26, and supplies control jet 27. This bias initially deflects the power stream from power nozzle 28 through outlet 29, which feeds chamber 30 in a double acting control valve 31, for the specific purpose of retaining this valve in an open condition. This valve is preset such that, under normal operating conditions, element switching cannot take place, but as soon as bounce" occurs, the pressure wave through control jet 23 will overcome the bias, and switch the power stream to flow through outlet 32. The power stream then passes through line 33 feeding chamber 34 of valve M, which, tending now to close, reduces the flow of pressurized fluid through conduit 11.

This partial drop in supply pressure is sufficient to substantially eliminate this bounce" characteristic and, thereafter assists in controlling the support pad pressure at an operational level. As can be seen from FIG. I, the system is vented at 35 and 36 through restrictors 37 and 38. This prevents back pressures from decreasing the efficiency of element 13. Restrictors 39 and 40 are positioned in control lines 2ll and 22 to adjust the control stream, but it will be obvious that these may be dispensed with, or others introduced throughout the circuit, as required.

Whilst it is envisaged that on a multi-pad arrangement, one such system, effective on one of the support pads, may be sufficient to overcome bounce," a more sophisticated arrangement can be seen in FIG. 2. Here we have a four-pad hover pallet, the first element 45 of a three-stage proportional amplifier is permitted to sense pressure fluctuations from pads 41 and 42 in a similar manner to that previously described in relation to element 13 of FIG. 1. Pressure fluctuations occurring in either pads 43 or 44 are sensed by elements 46 and 417 respectively. The preset bias pressure is, for convenience, effective on element 47, thus maintaining the valve 31 in the open condition.

In this system, irrespective ofin which pad a bounce" condition originates, one of the three elements will control.

A third embodiment is shown in FIG. 3, and utilizes a single fluidic element 48. The difference in this system over that previously described, is that the element does not sense pressure change from within the fluid cushion, but senses the movement of a sprung mass 49 in relation to vertical oscillations of the platform 1 caused by pressure variations within the supporting cushion.

When the load pallet starts to bounce the mass 49 oscillates on its spring mounting 50 at the same frequency. This varies the gap 51 between a pad valve .52 and its seating 53. The initial gap is maintained by a small spring 54, which also acts as a resilient mount for pad valve 52 on its seating 53. The element 48, as in previous embodiments, obtains its power from a tapping off the main supply conduit through supply line 55 to power nozzle 56. Control lines 57 and 58 are bled from the power supply via two restrictors 59 and 60. Restrictor 60 is made adjustable such that it provides a bias control stream to control jet 61, initially switching the power stream through outlet 62 to keep valve 31 open. When mass 49 oscillates at a critical frequency, pulses generated at the pad valve are transmitted to control jet 63, which overcomes the bias through control jet 61 and switches the power stream through outlet 64. This signal thereafter tends to close the valve 31 and reduce the main supply flow to the support cushions.

Additional stages of amplification incorporating feedback circuits, resistors, and extra accumulators, may be added as required.

The valve 31 is shown separate from the main supply control valve (not shown) which is operated generally by the pallet operator. This, however, need not be the case, the signals from the amplifier could be fed directly into the main supply control valve, carrying out the necessary control without the requirement of an additional valve.

Any known suitable form of fluidic element may be substituted for the device disclosed.

FIGS. 4, and 6 are introduced to show that the control system of the present invention can be utilized in other than a simple load pallet arrangement.

In FIG. 4, an air cushion vehicle is shown where the supporting cushion is bounded by a flexible skirt 70 and divided into a number of separate compartments 7] by longitudinally and laterally extending wall members 72 and 73. The control system preferably would employ a pressure sensor positioned in each compartment, and the fluidic arrangement would be similar to that disclosed in FIG. 2.

In FIG. 5, a I-Iovercraft having a multiplicity of support cushions is disclosed. Pressurized fluid is supplied to each air cushion 74, which is bounded by a skirt member. Sensors may be employed within each cushion area, as previously described.

Finally, in FIG. 6, a tracked air cushion vehicle is shown which utilizes the hover pallet principle. In the arrangement shown support is achieved by diaphragm type pallets 75; these could extend the entire length of the vehicle, on either side, or the support system could include a large number of such supporting diaphragms. The control system of the invention would substantially stabilize the vehicle and maintain an even distribution of fluid to each support cushion.

While the three embodiments disclose a control for hover pallets, it must be understood that such a system could equally be useful on large Hovercraft, ground effect machines or tracked air cushion vehicles, especially those utilizing a multiplicity of independent air cushions, or single compartmented air cushions.

With reference to FIG. 7, wherein a fully vented jet interaction beam deflection proportional amplifier is depicted, a power stream is fed into power nozzle 65 and control streams are fed into control jets 66 and 67. Items 68 and 69 are vents and 70 and 71 are outlets. Variable deflection of the power stream from power nozzle 65 is achieved within the amplifier in response to changes in control stream energies. When there is a difference of pressure between the control streams, deflection will cause more of the power stream to flow into one of the outlets than the other. Vents 68 and 69 vent the power stream under maximum and overload conditions and when the load is zero.

The vortex amplifier or valve shown in FIG. 7A, also suitable for use in the invention, operates as follows: The power stream 72 is introduced through power nozzle 73 at the outer wall of the vortex chamber, and is orientated to flow radially inwards towards the center outlet 74. The control jet 75 is located near the power nozzle 73 and the control stream is directed perpendicularly against the power stream 72.

If no control stream is present the power stream flows directly to the outlet, giving maximum output. When a control stream is introduced it deflects the power stream 72 away from its radial path to establish a spiral pattern as shown. The deflection of the power stream, and subsequent formation of the vortex, lengthens the flow path and increases the acceleration of the power stream, which increases the pressure drop, the output being a variable factor decreasing with the increase of control pressure.

We claim as our invention:

1. In a fluid cushion supported load bearing platform having a platform member and means for supplying pressurized fluid to a supporting cushion area beneath said platform so as to form and maintain the supporting cushion, a pressure control system to obviate parasitic oscillations in the supporting cushion comprising sensor means responsive to pressure variations in said supporting cushion for emitting output signals in accordance with such pressure variations, and fluidic control means responsive to signals from said sensor means for reducing the supply of pressurized fluid to said supporting cushion in response to predetermined signals from said sensor means, said fluidic control means comprising, in combination, fluid amplifier means and pneumatically operated valve means, said fluid amplifier means being responsive to signals from said sensor means and providing pneumatic control outputs to operate said valve means, said fluid amplifier means includes a fluidic element having a power nozzle for emitting a power stream, at least one outlet aperture, and at least one control jet for emitting a control stream to interact with the power stream and vary its path relative to said at least one outlet aperture so as to vary the output therefrom.

2. Apparatus as claimed in claim 1 wherein said sensor means communicates with said control jet of said amplifier means, and emits fluidic signals to vary the control stream and hence control said power stream.

3. Apparatus as claimed in claim 2 wherein said sensor means is a pneumatic sensor and directly senses pressure variations occurring in said supporting cushion.

4. Apparatus as claimed in claim 2 wherein said sensor means comprises means for sensing vertical oscillations of said platform caused by pressure variations in said supporting cushion.

5. A pressure control system as claimed in claim 1 wherein the sensor means is positioned within the area bounded by the platform and a cushion retaining member.

6. A pressure control system as claimed in claim 1 wherein said sensor means comprises a sensing device responsive to vertical oscillations of the platform caused by pressure fluctuations within the fluid support system for emitting signals indicative of pressure fluctuations to the fluidic control means.

7. A pressure control system as claimed in claim 6 wherein the sensing device is freely supported from the platform by first spring means, the sensing device includes spring loaded valve means, and fluid supply means interconnecting the sensing device with the fluidic control means and a source of pressurized fluid.

8. A pressure control system as claimed in claim 1 wherein the said fluid amplifier means includes a fluidic element comprising a fully vented jet interaction beam deflection proportional amplifier.

9. A pressure control system as claimed in claim 1 wherein the said fluid amplifier means includes a fluidic element comprising a vortex amplifier.

10. A pressure control system as claimed in claim 1 wherein a fluid feedback network is incorporated within the system to stabilize the output from the fluidic element. 

1. In a fluid cushion supported load bearing platform having a platform member and means for supplying pressurized fluid to a supporting cushion area beneath said platform so as to form and maintain the supporting cushion, a pressure control system to obviate parasitic oscillations in the supporting cushion comprising sensor means responsive to pressure variations in said supporting cushion for emitting output signals in accordance with such pressure variations, and fluidic control means responsive to signals from said sensor means for reducing the supply of pressurized fluid to said supporting cushion in response to predetermined signals from said sensor means, said fluidic control means comprising, in combination, fluid amplifier means and pneumatically operated valve means, said fluid amplifier means being responsive to signals from said sensor means and providing pneumatic control outputs to operate said valve means, said fluid amplifier means includes a fluidic element having a power nozzle for emitting a power stream, at least one outlet aperture, and at least one control jet for emitting a control stream to interact with the power stream and vary its path relative to said at least one outlet aperture so as to vary the output therefrom.
 2. Apparatus as claimed in claim 1 wherein said sensor means communicates with said control jet of said amplifier means, and emits fluidic signals to vary the control stream and hence control said power stream.
 3. Apparatus as claimed in claim 2 wherein said sensor means is a pneumatic sensor and directly senses pressure variations occurring in said supporting cushion.
 4. Apparatus as claimed in claim 2 wherein said sensor means comprises means for sensing vertical oscillations of said platform caused by pressure variations in said supporting cushion.
 5. A pressure control system as claimed in claim 1 wherein the sensor means is positioned within the area bounded by the platform and a cushion retaining member.
 6. A pressure control system as claimed in claim 1 wherein said sensor means comprises a sensing device responsive to vertical oscillations of the platform caused by pressure fluctuations within the fluid support system for emitting signals indicative of pressure fluctuations to the fluidic control means.
 7. A pressure control system as claimed in claim 6 wherein the sensing device is freely supported from the platform by first spring means, the sensing device includes spring loaded valve means, and fluid supply means interconnecting the sensing device with the fluidic control means and a source of pressurized fluid.
 8. A pressure control system as claimed in claim 1 wherein the said fluid amplifier means includes a fluidic element comprising a fully vented jet interaction beam deflection proportional amplifier.
 9. A pressure control system as claimed in claim 1 wherein the said fluid amplifier means includes a fluidic element comprising a vortex amplifier.
 10. A pressure control system as claimed in claim 1 wherein a fluid feedback network is incorporated within the system to stabilize the output from the fluidic element. 